The present invention relates generally to removal systems, such as those used in gasification systems, and more particularly, to acid gas removal systems used in chemical plants producing chemicals from syngas generated by gasification and in integrated gasification combined-cycle (IGCC) power generation plants that combust syngas generated by gasification.
Most known IGCC plants include a gasification system that is integrated with at least one power-producing turbine system. Also, many known chemical production facilities include a similar gasification system. For example, at least some known gasification systems convert a mixture of fuel, air or oxygen and nitrogen, steam, water, and/or CO2 into a synthesis gas, or “syngas.” The syngas is channeled either to the combustor of a gas turbine engine, which powers an electrical generator that supplies electrical power to a power grid, or channeled to downstream reactors to produce chemicals. Exhaust from at least some known gas turbine engines is supplied to a heat recovery steam generator (HRSG) that generates steam for driving a steam turbine. Power generated by the steam turbine also drives an electrical generator that provides electrical power to the power grid.
At least some known gasification systems produce a “raw” syngas fuel that includes gaseous byproducts such as carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), carbonyl sulfide (COS), and hydrogen sulfide (H2S). The H2S and COS are typically referred to as acid gases. Moreover, the CO2, H2S, and COS, generated with the use of gasification technology, are generally removed from the raw syngas fuel to produce a “clean” syngas fuel for downstream process reactors or combustion within the gas turbine engines. Within known systems, such acid gas removal (AGR) is performed with an integrated CO2/AGR system that removes a significant portion of the CO2, H2S, and COS with circulated refrigerated solvents. Sulfur collected by the AGR system is typically recovered by a sulfur recovery subsystem. CO2 is disposed of by one of recycling to the gasifier, sequestration, and deposition.
Many known gasification systems include a gasifier that is operated at low pressures, i.e., within a pressure range of between approximately atmospheric [(101 kilopascal) (kPa) (14.7 pounds per square inch absolute (psia)] and approximately 4,137 kPa (600 psia). Gas generated within the gasifier is channeled to an integrated CO2/AGR system within a pressure range of between approximately 2,068 kPa (300 psia) and approximately 3,447 kPa (500 psia). Many of these known gasification systems use a booster compressor downstream of the integrated CO2/AGR system to channel the clean syngas fuel to the combustion turbines.
Capture and removal of CO2, H2S, and COS is a function of a pressure of the gases channeled within the integrated CO2/AGR system and an amount of solvent circulated therein. Therefore, in many known low pressure gasification systems, improvements in an effectiveness and an efficiency of capture and removal of CO2, H2S, and COS from the raw syngas may be limited to increasing solvent flows and/or increasing gasification pressure. However, increasing solvent flows increases auxiliary power loads and associated operating costs. Moreover, increasing the operating pressure of the gasifier may result in an increase in costs of material used to fabricate the gasifier, for example, installation of high-end corrosion-resistant metals for cladding inside the gasifier to increase a tolerance of the gasifier to acidic environments at dew point conditions. Also, increasing the gasifier pressure may increase auxiliary power costs due to increased pressure requirements for channeling liquids and gases throughout the gasification process. In addition, such a retrofit to a higher pressure gasifier may not be available for gasification systems that are limited in operating pressure due to constraints in the feed system, as may be imposed by the use of lock hoppers.